Hack installation:

1. Download and install the file hide-xfields-from-url.xml in the Engine Control Panel's External Plugins Management:
2. Specify rules (above category rules):

NGINX (nginx.conf -> server -> location):

Find:

rewrite "^/([^.]+)/page/([0-9]+)(/?)+$" /index.php?do=cat&category=$1&cstart=$2 last; 
rewrite "^/([^.]+)(/?)+$" /index.php?do=cat&category=$1 last;

Insert above:

location / {

        rewrite "^/(.*[\.]+.*)/page/([0-9]+)(/?)+$" /index.php?do=xfsearch&xf=$1&cstart=$2  last; 
        rewrite "^/(.*[\.]+.*)/?$" /index.php?do=xfsearch&xf=$1 last;

 } 

Or if you are using APACHE2, find the file (.htaccess) in the root of your site Attention! Before modifying the file, be sure to save a copy:

Find:

RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^.]+)/page/([0-9]+)(/?)+$ index.php?do=cat&category=$1&cstart=$2 [L]

Insert above:

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*[\.]+.*)/page/([0-9]+)(/?)+$ index.php?do=xfsearch&xf=$1&cstart=$2 [L]
RewriteRule ^(.*[\.]+.*)/([^/]*)(/?)+$ index.php?do=xfsearch&xf=$1 [L]

3. Remove redirects from .htaccess related to xfsearch

RewriteRule ^xfsearch/(.*)/page/([0-9]+)(/?)+$ index.php?do=xfsearch&xf=$1&cstart=$2 [B,L]
RewriteRule ^xfsearch/(.*)/?$ index.php?do=xfsearch&xf=$1 [B,L]

4. Introduce redirection for old xfsearch (for example, to the main page)

Find:

RewriteRule ^page/([0-9]+)(/?)$ index.php?cstart=$1 [L]

Insert above:

RewriteRule ^xfsearch/(.*)$ / [R=301,L] 

or to a new page:

RewriteRule ^xfsearch/(.*)$ /$1 [R=301,L] 

Add redirects to ensure that xfsearch works for values with dots. All new cross additional fields will work and will not require adding a rule to .htaccess.